Present-day aircraft are making more and more use of electrical flight control systems. Such systems comprise flight control members including a movable airfoil, such as an aileron, a flap, or an elevon, associated with two electric motors, each connected to a power supply circuit controlled using control signals coming from flight controls operated by the pilot of the aircraft. The two motors are used in alternation such that in the event of one of the motors failing, the other motor can be used as a replacement.
Each power supply circuit comprises a plurality of inverter bridges each made up of three bridge arms, themselves provided with means for connecting each of them to a respective winding of the motor. Each inverter bridge arm comprises in series a first insulated gate bipolar transistor and a second insulated gate bipolar transistor that are connected to a controller, itself connected to the piloting instruments.
When one of the motors is not used, it is disconnected from the power supply circuit, but it is nevertheless expected to exert a force on the movable airfoil so as to damp its movement.
A dedicated damper circuit is thus provided between the motor and the power supply circuit for dissipating the energy it produces when it is driven by the movable airfoil under drive from the other motor or under a dynamic effect. Such a damper circuit is connected to the motor via an electromechanical relay that connects the motor selectively to the power supply circuit or to the damper circuit. Such a relay presents several drawbacks: a short lifetime, in particular because of switching under load, unreliable ability to withstand vibration, and weight and volume that are not very compatible with the requirements to save weight and space that are imposed by the design constraints on aircraft. A failure of the main member of the relay (coil or control) also leads to losing all of the capacity for damping.